1. Field of the Invention
The present invention relates to a supercharged internal combustion engine with a supercharger controlled in accordance with the condition of operation of the engine.
2. Description of the Prior Art
Various types of superchargers including mechanically-driven superchargers and turbo superchargers have been known. These conventional superchargers are operative in both throttle part-open and full-open engine operating ranges so as to attain an increased engine output in the throttle full-open engine operating range. An exhaust or intake bypass passage is employed to avoid supercharging at an unduly high pressure.
However, it is not good policy to operate the supercharger over the entire engine operation ranges. Namely, in case of a turbo supercharging system, the flow of pressurized air discharged from the supercharger is restricted or throttled by the throttle valve of the engine during the throttle part-open engine operation to render the operation of the supercharger meaningless. At the same time, the exhaust pressure of the engine is increased, as the exhaust gases are forced to pass through and drive the supercharger, so that the intake efficiency of the engine is considerably lowered to decrease the engine output. Further, the supercharging over the entire engine operation ranges subjects the supercharger itself and the intake and exhaust systems to continuous load. This is quite inconvenient from the view point of the durability of the supercharger and the intake and exhaust systems.